libprocessgroup: Move CgroupSetupCgroups() to libprocessgroup_setup

Only init uses SetupCgroups. This functionality is
moved from libprocessgroup to its own library, and only
init links to it.

Also, merge CgroupSetupCgroups() with CgroupMap::SetupCgroups()
because the former is just an alias of the latter, and
CgroupMap does not belong to libcgrouprc_setup.

Test: boots
Bug: 123664216
Change-Id: I941dc0c415e2b22ae663d43e30dc7a464687325e
Merged-In: I941dc0c415e2b22ae663d43e30dc7a464687325e
diff --git a/init/init.cpp b/init/init.cpp
index cdec41c..1792f28 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -45,6 +45,7 @@
 #include <libavb/libavb.h>
 #include <libgsi/libgsi.h>
 #include <processgroup/processgroup.h>
+#include <processgroup/setup.h>
 #include <selinux/android.h>
 
 #ifndef RECOVERY